Hormonal changes from intermittent fasting Original paper

Intermittent fasting (IF) is characterized by periods of not eating and is comparable to caloric restriction for weight loss and cardiometabolic health. A previous Editor’s Pick provided a summary of the different types of IF and their cardiometabolic benefits.

Preliminary research suggests that IF may negatively influence hormones and growth and reproduction, but a review of human studies was needed.

This review evaluated 7 human IF trials (3 in women, 4 in men; 5 on time-restricted feeding, 1 on the 5:2 diet, and 1 compared eating 50% of daily calories at breakfast to eating 50% of daily calories at dinner, which technically isn’t IF) for insight into whether IF may influence hormones.

All three studies (one of which was the study that wasn’t an IF trial) in women suggested that IF can decrease androgens (i.e., “male” sex hormones) and increase sex hormone-binding globulin (which transports hormones to the target tissues) concentrations in premenopausal women (1 study) and those with polycystic ovarian syndrome (PCOS; a condition characterized by higher-than-normal androgens). Fasting did not appear to influence other reproductive hormones such as estrogen, gonadotropins, and prolactin, although the results from one study suggested that eating more than 50% of daily kilocalories at dinner can increase estrogen levels in women with PCOS.

All four studies in men (young, lean, and physically active) suggested that IF can decrease testosterone, without changing sex hormone-binding globulin or muscle mass and strength. However, it’s worth noting that in each of these studies, the participants lost a significant amount of body weight.

The authors went on to discuss how IF has been shown to improve the gut microbial profile and circadian alignment, which may indirectly influence hormone levels.

Androgen deficiency in men and androgen excess in women are associated with metabolic syndrome and type 2 diabetes.^[1]